This invention relates to the precursors for manufacturing dielectric materials with low dielectric constants for use in the manufacture of semiconductor integrated circuits. The invention also relates to the polymers made from these precursors, the processes used to make polymers, and the integrated circuits made from these polymers.
As integrated circuits (ICs) have become progressively more microminiaturized to provide higher computing speeds, the low dielectric constant polymers used in the manufacturing of the ICs have proven to be inadequate in several ways. Specifically, they have not had sufficient thermal stability, generate toxic byproducts, are inefficient to manufacture, and the dielectric constants are too high.
During the past few years, several types of precursors have been used to manufacture polymers with low dielectric constants for use in manufacture of integrated circuits (IC). Transport Polymerization (TP) and Chemical Vapor Deposition (CVD) methods have been used to deposit low dielectric materials. The starting materials, precursors and end products fall into three groups, based on their chemical compositions. The following examples of these types of precursors and products are taken from Proceedings of the Third International Dielectrics for Ultra Large Scale Integration Multilevel Interconnect Conference (DUMIC), Feb. 10-11 (1997).
I. Modification of SiO2 by Carbon (C) and Fluorine (F)
The first method described is the modification of SiO2 by adding carbon and/or fluorine atoms. McClatchie et al., Proc. 3d Int. DUMIC Conference, 34-40 (1997) used methyl silane (CH3xe2x80x94SiH3) as a carbon source, and when reacted with SiH4 and the oxidant H2O2 and deposited using a thermal CVD process, the dielectric constant (K) of the resulting polymer was 3.0. However, this K is too high to be suitable for the efficient miniaturization of integrated circuits.
Sugahara et al., Proc. 3d Int. DUMIC Conference, 19-25 (1997) deposited the aromatic precursor, C6H5xe2x80x94Sixe2x80x94(0CH3)3 on SiO2 using a plasma enhanced (PE) CVD process that produced a thin film with a dielectric constant K of 3.1. The resulting polymer had only a fair thermal stability (0.9% weight loss at 450xc2x0 C. in 30 minutes under nitrogen). However, the 30 min heating period is shorter than the time needed to manufacture complex integrated circuits. Multiple deposition steps, annealing, and metalizing steps significantly increase the time during which a wafer is exposed to high temperatures. Thus, this dielectric material is unsuitable for manufacture of multilevel integrated circuits.
Shimogaki et al., Proc. 3Int. DUMIC Conference, 189-196 (1997) modified SiO2 using CF4 and SiH4 with NO2 as oxidant in a PECVD process. The process resulted in a polymer with a dielectric constant of 2.6, which is lower than that of SiO2.
However, one would expect low thermal stability due to low bonding energy of sp3Cxe2x80x94F and sp3Cxe2x80x94Si bonds (BE=110 and 72 kcal/mol., respectively) in the film. The low thermal stability would result in films which could not withstand the long periods at high temperatures necessary for integrated circuit manufacture.
II. Amorphous-Carbon (xcex1C)- and Fluorinated Amorphous Carbon (F-xcex1C)-Containing Low Dielectric Materials
The second approach described involves the manufacture of xcex1-carbon and xcex1-fluorinated carbon films. Robles et al., Proc. 3d Int. DUMIC Conference, 26-33 (1997) used various combinations of carbon sources including methane, octafluorocyclobutane and acetylene with fluorine sources including C2F6 and nitrogen trifluoride (NF3) to deposit thin films using a high density plasma (HDP) CVD process.
The fluorinated amorphous carbon products had dielectric constants as low as 2.2 but had very poor thermal stability. These materials shrank as much as 45% after annealing at 350xc2x0 C. for 30 minutes in nitrogen.
One theory which could account for the low thermal stability of the fluorinated amorphous carbon products is the presence of large numbers of sp3Cxe2x80x94F and sp3Cxe2x80x94sp3C bonds in the polymers. These bonds have a bonding energy of 92 kcal/mol. Thus, the films can not withstand the long periods of high temperatures necessary for IC manufacture.
III. Fluorinated Polymers
The third approach described uses fluorinated polymers. Kudo et al., Proc. 3d Int. DUMIC Conference, 85-92 (1997) disclosed polymers made from C4F8 and C2H2 with a dielectric constant of 2.4. The polymers had a Tg of 450xc2x0 C. (Kudo et al., Advanced Metalization and Interconnect Systems for ULSI Applications; Japan Session, 71-75 (1996)).
However, despite its low leakage current due to presence of sp3Cxe2x80x94F bonds, a low thermal stability can be expected due to presence of sp3Cxe2x80x94F and sp3Cxe2x80x94sp3C bonds in the films. Thus, like the F-xcex1C-containing polymers discussed above, these fluorinated polymers are unable to withstand the prolonged high temperatures necessary for IC manufacture.
LaBelle et al, Proc. 3d Int. DUMIC Conference, 98-105 (1997) made CF3xe2x80x94CF(O)xe2x80x94CF2 polymers using a pulsed plasma CVD process, which resulted in a polymer film with a dielectric constant of 1.95. However, in spite of the low K, these polymer films would be expected to have low thermal stability due to presence of sp3Cxe2x80x94sp3C and sp3Cxe2x80x94O bonds in these films which have bonding energies of 85 kcal/mol.
Therefore, none of the previously described low dielectric materials have suitably low K and high thermal stability necessary for IC manufacturing.
Wary et al, (Semiconductor International, June 1996, 211-216) used the precursor, (xcex1, xcex1, xcex11, xcex11) tetrafluoro-di-p-xylylene) or {xe2x80x94CF2xe2x80x94C6H4xe2x80x94CF2xe2x80x94}2 Parylene AF-4(trademark), which contains a non-fluorinated aromatic moiety, and a thermal CVD process to manufacture Parylene AF-4(trademark) which has the structural formula: {xe2x80x94CF2xe2x80x94C6H4xe2x80x94CF2xe2x80x94})n. Films made from Parylene AF-4(trademark) have a dielectric constant of 2.28 and have increased thermal stability compared to the above-mentioned dielectric materials. Under nitrogen atmosphere, a polymer made of Parylene AF-4(trademark) lost only 0.8% of its weight over 3 hours at 450xc2x0 C.
However, in spite of the advantages of conventional poly(para-xylylenes), there are disadvantages of the known methods of their manufacture. First, the manufacture of their precursors is inefficient because the chemical reactions have low yields, and the process is expensive and produces toxic byproducts. Further, it is difficult to eliminate redimerization of the reactive intermediates. When deposited along with polymers, these dimers decrease the thermal stability and mechanical strength of the film.
Thus, the prior art contains no examples of dielectric material precursors for semiconductor manufacture which have desired properties of low dielectric constant, high thermal stability, and low cost.
The present invention is directed to overcoming the disadvantages of the prior art.
Accordingly, one object of the invention is to provide precursor materials which can be used to manufacture products including polymers with low dielectric constants for IC manufacture.
Another object of the invention is to provide precursors which can be manufactured into products which have high thermal stability.
Yet another object of the invention is to provide precursors which can be polymerized as thin layers on a substrate.
An additional object of the invention is to provide precursor materials which are inexpensive.
A further object is to provide materials which can be made into products with high efficiency.
An additional object of the invention is to provide precursors which can be made into dielectric materials which can be easily and accurately shaped after manufacture.
The invention includes novel precursors containing a fluorinated silane, a fluorinated siloxane or a fluorocarbon each containing a fluorinated aromatic moiety. The precursors are suitable for making polymers with low dielectric constants and high thermal stability. The polymers can be used for making integrated circuits.
Additionally, the invention includes methods for making polymers for integrated circuit manufacture using novel fluorinated silanes, fluorinated siloxanes, or fluorocarbons, each containing a fluorinated aromatic moiety.
Furthermore, the invention includes integrated circuits comprising low dielectric constant polymers made using fluorinated silanes, fluorinated siloxanes, or fluorocarbons, each containing a fluorinated aromatic moiety.
Accordingly, one aspect of the invention comprises precursors for using in manufacturing polymers with low dielectric constants which are useful in the manufacture of integrated circuits (ICs).
Another aspect of the invention comprises precursors for use in manufacturing polymers with high thermal stability which are useful in the manufacture of ICs.
Another aspect of the invention comprises methods for reacting the precursors and depositing them as thin films on substrates for IC manufacture.
Yet another aspect of the invention comprises the deposited thin film made using the novel precursors and methods for their reaction and deposition.
Another aspect of the invention is the integrated circuits comprised of thin films derived through the reaction and deposition of the novel precursors.
Other objects, aspects and advantages of the invention can be ascertained from the review of the additional detailed disclosure, the examples, the figures and the claims.